"A pulmonary embolism kills by effectively shutting off the flow of blood from the right heart to the lungs," said Dr. Andrew Hurwitz, head of cardiothoracic surgery at Glendale Memorial Hospital.
A pulmonary embolism is a blood clot in the lungs. It usually starts somewhere in the leg and travels through the heart to the lungs. Dr. Hurwitz, who is not treating Williams, says blood clots in the legs or deep vein thrombosis (DTV) can happen to anyone despite your age and fitness level.
It's the same condition that killed news correspondent David Bloom.
"Deep vein thrombi, or DTVs as they're called, are actually very common and they're surprisingly silent in that there's very little in the way of symptoms or signs," said Hurwitz. "Some people have swelling in the legs, pain or warmth in the leg."
Leg vein clots are quite common in someone who's had surgery or spends a great deal of time traveling.
Reports say Williams had foot surgery to treat an injury and she also spends a lot of time on airplanes.
Dr. Hurwitz says once someone is diagnosed with DVT they're treated with blood thinners. If that doesn't work, doctors have to put in a filter to prevent the clot from traveling to the heart.
"It's inserted into the femoral vein and then positioned in the inferior vena cava in such a way as to prevent the clot from reaching the heart. It looks like an umbrella," said Dr. Hurwitz.
In very rare cases, open heart surgery is required to remove the clot.
Doctors say people can recover from a pulmonary embolism quite well.
Dr. Hurwitz says the best way to prevent a clot is to try and prevent them from occurring in your extremities by being as mobile as possible following surgery. If you're on a long plane ride, get up or move your legs every 15 minutes. And if you're on a road trip, stop and take some walking breaks.
A spokesperson for Williams said she is recovering at home and is being monitored very closely. In a statement, Williams said she hopes to be back on the court by early summer.